As shown in FIGS. 1a and 1b, a conventional camera module 100 includes a lens assembly 110, a motor assembly 120 and an image sensor assembly 130. The assembly process of the camera module 100 includes the following steps.
Step 1, mounting an image sensor chip 131 on a PCB 132;
Step 2, mounting a filter 133 and a filter holder 134 on the PCB 132;
Step 3, joining the bottom of the motor assembly 120 on the filter holder 134;
Step 4, installing the lens assembly 110 in the motor assembly 120.
A conventional lens assembly 110 includes a lens barrel 111 and a lens holder 112, multiple lens are stacked in the lens barrel 111, and the lens barrel 111 and the lens holder 112 are connected together by means of screw thread.
By this token, during the assembly process of the camera module, a lot of components are to be assembled which cumulates more and more assembly tolerance to degrade the imaging quality of the camera, for example the in-focus position deviates from the image center, and the definition of the image corners are uneven. Especially with the increasing resolution of the image sensor and the decreasing unit cell size of the image sensor developing, how to accurately locate the lens assembly to the image sensor to achieve an accurate optical axis alignment becomes a critical issue.
The optical axis alignment of the conventional camera module is achieved by an automatic alignment device (such as active alignment equipment) which can real time detect planar angle of image sensor to align the optical axis of the lens with the center of the image sensor, in order to reduce the assembly tolerance and improve the quality of the camera module. However, such an automatic alignment device is quite expensive, which directly restricts the development of the small and medium manufacturers.
Thus it is desired to provide an improved lens assembly, a camera module and assembly methods to overcome the drawbacks mentioned above.